In recent years piperazine derivatives have emerged as a new class of designer drugs, gaining popularity especially among young people in the dance music scene where they are commonly known as ‘party pills’. They are often marketed as ‘natural’ or ‘herbal’ products but are in fact entirely synthetic chemicals. Coupled with their ease of availability and varying legal status across the globe this can create the misconception that these drugs are safe and without the risks commonly associated with traditional street drugs. Piperazine derivatives are usually found in illicit dosage forms as either tablets or capsules, but loose powders and more rarely solutions also occur. The tablets often carry logos similar to those seen on ecstasy tablets and they are often misleadingly sold as ecstasy or as apparent ‘safer’ and ‘legal’ alternatives. Their name derives from the piperazine heterocycle which is a common feature and they can be divided into two sub-classes; the benzylpiperazines, such as 1-benzylpiperazine (BZP) itself, and the phenylpiperazines which include 1-(3-chlorophenyl)piperazine (mCPP), 1-(4-methoxyphenyl)piperazine (MeOPP) and 1-(3-Trifluoromethylphenyl)piperazine (TFMPP) (FIG. 1 shows the structure of these and other phenylpiperazine derivatives).
The phenylpiperazines are extensively metabolised with the major metabolic reaction being metabolic alteration of the aromatic ring, either by hydroxylation (mCPP, TFMPP) or by O-demethylation of the methoxy moiety (MeOPP) (Maurer et al., 2004). Metabolic degradation of the piperazine moiety to the corresponding ethylenediamine or aniline derivatives is also observed. Metabolic phase II reactions are partial glucuronidation or sulphation of the phenolic metabolites, methylation of the catechols and partial acetylation of the aniline derivatives (Maurer et al., 2004).
One of the most widespread phenylpiperazines, mCPP, is an active metabolite of the antidepressant drug trazodone and related therapeutic drugs. mCPP is a 5-HT receptor agonist with stimulant and hallucinogenic properties similar to 3,4-methylenedioxy-N-methamphetamine (MDMA; the active ingredient of ecstasy), unlike MDMA it does not cause an increase in heart rate or blood pressure. There are two positional isomers of mCPP, 1-(4-chlorophenyl)piperazine and 1-(2-chlorophenyl)piperazine. By 2006, it was estimated that almost 10% of illicit tablets sold in the EU, as part of the illicit ecstasy market, contained mCPP (European Monitoring Centre for Drugs and Drug Addiction, EMCDDA). It has now been suggested from anecdotal reports of users online that at least 50% of ecstasy pills sold in the UK and the rest of Europe may contain mCPP as the primary active ingredient (EMCDDA). Following oral administration of mCPP to healthy human male volunteers, the elimination half-life ranges from 2.6 to 6.1 hours with a wide variation in peak blood levels and bioavailability (EMCDDA). The negative effects of mCPP, often typical of a serotonin syndrome, include anxiety, dizziness, confusion, shivering, sensitivity to light and noise, fear of losing control, migraine and panic attacks (EMCDDA).
Another piperazine derivative commonly found in party pills is TFMPP. TFMPP acts as a non-selective serotonin receptor agonist, in addition to boosting synaptic serotonin levels by blocking serotonin reuptake and increasing its release (Nikolova & Danchev, 2008). It has no therapeutic use, but has been sold as a recreational drug used as a ‘legal’ alternative to illicit drugs such as Lysergic acid diethylamide (LSD) and MDMA. TFMPP has properties similar to the stimulant effects of ecstasy, but taken in larger doses it promotes hallucinogenic reactions (Nikolova & Danchev, 2008). It is nearly always found in combination with BZP, with which it has a synergistic relationship. The BZP/TFMPP combination leads to increases in dopamine and serotonin levels greater than those observed when either is taken individually (Baumann et al., 2005). This allows manufacturers to lower the dose of each without compromising the effect of the drugs. TFMPP has been shown to be extensively metabolised (Staack et al., 2003), mainly by hydroxylation of the aromatic ring and by degradation of the piperazine moiety to N-(3-trifluoromethylphenyl)ethylenediamine, N-(hydroxyl-trifluoromethylphenyl)ethylenediamine, 3-trifluoromethylaniline, and hydroxyl-3-trifluoromethylaniline, while phase II reactions included glucuronidation, sulphation and acetylation of phase I metabolites.
MeOPP (synonyms: 1-(4-methoxyphenyl)piperazine, Paraperazine, 4-MeOPP) is another piperazine derivative which has been sold as an ingredient in ‘Party Pills’, initially in New Zealand and subsequently in other countries around the world (Maurer et al., 2004). It has similar effects to those of ecstasy although much less potent (Nikolova & Danchev, 2008). Like TFMPP it is commonly found in combination with BZP to enhance its effects. Indeed various mixtures of piperazine derivatives have been observed with most consisting of variations of BZP, TFMPP, mCPP and Dibenzylpierazine (DBZP), sometimes mixed with other substances such as amphetamine, cocaine, ketamine, MDMA and caffeine (EMCDDA; Drug Enforcement Administration [DEA] report 2009). With the increasing criminalisation of phenylpiperazine derivatives such as those discussed above there is a need for a simple, rapid technique allowing for routine testing of these drugs.
Analytical methods which have been used to detect or determine piperazine derivatives include GC-MS and LC-MS (Staack & Maurer 2003; Antia et al., 2010). Peters et al., (2010) present a review of analytical toxicology of emerging drugs of abuse including piperazines. A disadvantage of mass spectrometry-based methods of detection is that they require expensive equipment and highly trained staff. Immunoassays are known in the art as relatively cost effective, simplistic and rapid alternatives to mass-spectrometry based analysis. A commercially available enzyme immunoassay test, the EMIT II plus Ecstasy Assay (SYVA/Dade Behring), has been shown to have cross-reactivity to TFMPP and mCPP at concentrations between 5,000-10,000 ng/ml (Logan et al., 2010). The manufacturers include no information for cross-reactivity with mCPP or TFMPP in kit inserts and detection levels of this kit are insufficient for testing purposes. International Patent Publication No WO2010142974 discloses antibodies and methods for differentiating between metabolic mCPP as a result of an individual taking antidepressant drugs and mCPP which is taken illicitly. However these antibodies are not cross-reactive to other phenylpiperazine derivatives. Hence there remains no readily-available screening test specific for phenylpiperazine derivatives and thus to solve this problem a cost effective and rapid method is required to detect and determine the range of phenylpiperazine derivatives found in designer drugs.